LONG TERM GOAL: Production of novel ketolide antibiotics with potent antibacterial activity against macrolide susceptible and resistant bacterial pathogens. PHASE I: We will develop a biological process for production of 15-methyl-6- deoxyerythronolide B, the precursor of 15-methylerythromycin A, through genetic engineering of the 6-deoxyerythronolide B polyketide synthase. This will be accomplished by optimizing the biosynthetic pathway of a substrate used to make the target compound in Streptomyces coelicor, a related actinomycete strain of Escherichia coli. That substrate will be used by an engineered 6-deoxyerythronolide B polyketide synthase to make 15-methyl-6-deoxyerythronolide B, which will be isolated and bioconverted to 15-methylerythromycins by a strain of Saccharopolyspora erythraea or directly to this compound by an engineered strain of Streptomyces fradiae that contains the genes for production of 15-methyl-deoxyerythronolide B and the 15- methylerythromycins. PHASE II: This process will be optimized for large scale production of 15- methyerythromycins that will be used to make ketolide antibiotics in sufficient amount for preclinical and clinical development. Kosan has discovered a lead ketolide in partnership with The R.W. Johnson Pharmaceutical Research Institute and expects that this compound or a close analog will be developed into a drug that is competitive with the two current front runners in this area. PROPOSED COMMERCIAL APPLICATIONS: There is a growing need to discover and develop noel antibiotics that can overcome resistance mechanisms. The proposed research will generate modified macrolide antibiotics which are effective against macrolide resistant organisms. Since world-wide sales of macrolide antibiotics exceed $3B per year, these new antibiotics should have significant commercial value.